From the past, with a working vehicle such as a construction machine or the like, a technique has been known in which a plurality of output modes are provided to the engine, and the user sets one of these output modes, according to the magnitude of the output which is required for working. For example, according to Patent Document #1, the working vehicle has two output modes: a power mode in which high output can be obtained, and a standard mode in which a lower output can be obtained.
The user sets one of these output modes manually by actuating a mode setting switch or the like. In other words, if the user has decided that the work which is henceforth to be performed is heavy work, then the user selects the power mode. Conversely, if the user has decided that the work which is henceforth to be performed is light work, then the user selects the standard mode.
An engine controller which controls the engine controls the output of the engine based on the command from the mode setting switch. In other words, in the standard mode, the output of the engine is limited so as to be less than or equal to a predetermined value, for example by restricting the fuel or the like. On the other hand, in the power mode, the engine controller imposes no particular limitation, so that the output of the engine is controlled so as to obtain any output up to its rated output or its maximum output.
By doing this, light work is performed with a small engine output, so that the amount of energy consumed is reduced, and it is possible to anticipate a reduction of the fuel consumption. And, by arranging not to impose any limitation on the output of the engine during heavy working, it is possible to obtain the required output for such working.
Patent Document 1: Japanese Patent Laid-Open Publication Heisei 8-218442.
However, there are problems with this prior art technique, as will now be explained.
That is to say, with a working vehicle, it is not the case that heavy working only, or light working only, is performed continuously; rather, it is usually the case that, during a series of working processes, heavy working and light working are performed alternatingly. For example, with a dump truck, loaded running in a state in which a load is loaded on the vehicle, and empty running in a state in which the load is discharged, are alternatingly repeated. This loaded running corresponds to heavy working while the empty running corresponds to light working.
According to the prior art, each time a change over takes place between heavy working and light working, the user must change over the output mode by actuating the mode setting switch. Since it is very troublesome to perform such a task during working, it often happens that the user does not change over the mode setting switch, so that working is performed with the output mode being constant at one of the power mode or the standard mode. As a result, the problems occur that it may be impossible to implement reduction of the fuel consumption, or that it may not be possible to obtain the required power output.